Jig systems have been used to hold building elements, such as wood boards, in proper position while the building elements are attached to each other to construct a roof support truss. Known jig systems typically employ a horizontal surface (such as a table) for resting the building elements thereon and a plurality of adjustable stops for indicating the proper positions of the building elements in the desired truss design and for holding the building elements in those positions until the elements can be secured together in a permanent manner. For each different truss design, the stops must be repositioned on the jig surface to reflect the different positions of the building elements. Computer programs have been developed to calculate, for various truss designs, the positions of the stops from a reference line, such as an edge of the table. Conventional practice has been to measure the positions of the stops from the reference line, manually move the stops to the positions, manually secure the stops in the desired positions, place the building elements on the table against the stops, fasten the building elements together, remove the completed truss, and then repeat the process by releasing and then re-securing the stops for each different truss design.
As there can be significant variation between the size and shape of roof support trusses used for the same building, a significant amount of the truss production time has been dedicated to resetting the positions of the stops, especially when only one or two trusses for each truss design are needed.
One approach has been to employ a system that automatically moves the jig stops, sometimes referred to as pucks, along slots in the horizontal surface of the truss assembly table. While in concept these systems can save time otherwise needed to measure, move and secure the stops on the table, there have been problems that have cropped up with these systems that make them less time saving and reliable as they could be for optimum efficiency.
Automatic jigging assemblies for use on truss assembly tables are described in U.S. Pat. Nos. 7,093,829; 6,712,347 and 6,889,324 to Fredrickson, et al. and U.S. Pat. Nos. 5,092,028 and 4,943,038 to Harnden. Each of these patents is hereby incorporated by references for any and all purposes.
The environment in which the jig systems are used is filled with debris and dust. Even when the building elements are cut and shaped at a location remote from the jig system, the building elements often carry sawdust and wood chips onto the surface of the table of the jig system. This debris falls or is pushed into the slot in which the puck moves. As each puck is typically mounted on a screw-threaded rod that is positioned below the puck in the slot, the debris often falls onto the rod. Since the rod rotates to move the puck, a rod caked with debris can hamper and even prevent movement of the puck along the rod. Thus, regular and frequent cleaning of the rod is needed to minimize the possibility of breakdowns of the system.
Further complicating this situation is the fact that the screw-threaded rods typically are covered with some type of lubricant to facilitate movement of the puck along the rod, and this often sticky lubricant holds the debris on the surface of the rod. The encrusted rod can carry the debris into the cooperating parts of the system, and cause additional friction and failure.
Still further exacerbating this problem in the known systems is the placement of the rod in a channel located below the slot with a closed bottom that holds the debris in close proximity to the rod, so that infrequent clearing of the channels can bring debris in contact with the rods from the bottom, as well as from the top as debris falls from the table surface.
Desired is a mechanism that will set up to build trusses automatically from computer instruction. The improved mechanism needs to set up quickly, run smoothly to reduce wear and tear on assembly components, and provide a means to prevent the maintenance problems that come from the accumulation of dirt and debris produced by the truss assembly operation in the mechanism. Finally, the system needs to be durable enough to withstand potential damage from the activities of truss assembly.
For truss jigging, the threaded rods that typically drive the pucks must be about 12 to 14 feet (3.65 to 4.27 meters) long. At this length, the threaded rod will sag under its own weight and, when turned at high revolutions per minute, will whip and gyrate violently unless it is properly constrained. Proper constraint is desired to achieve smooth operation of the rod.
The improved mechanism of the current invention will set up very quickly under control of a motion control computer which receives its set up data directly from truss engineering analysis software. The mechanics of the system run very smoothly and thereby greatly reduce the wear on all components, both electrical and mechanical. None of the components of the system will allow the accumulation of dirt and debris. Finally, extraordinarily severe abuse of the system will not cause failure. Details of how this is accomplished are given below.
Also desirable is a durable assembly that will resist extreme abuse from the truss assembly activity that occurs on the surface of the table. This abuse comes primarily from lumber that is being tossed onto the surface of the table and moved into position for truss assembly. Workers will also kick the pucks or hit them with hammers on occasion.
Thus, while the known systems for automatically positioning the pucks on the jig assembly table are an improvement over jig systems requiring manual positioning of the stops, there are significant problems that have arisen with the use of automatic systems.